Various widely enjoyed sports utilize objects (typically balls) that rebound from hard surfaces. These objects are mass produced, have a limited lifespan, and as they wear out are discarded. Many sports have standard guidelines stipulating how well the equipment utilized in the sport should perform, thus setting limits on when an object of play is no longer acceptable for use in sanctioned competition.
Tennis provides the best example here. The International Tennis Federation (ITF) is a governing body having one such standard for tennis balls. The tennis ball must satisfy a number of criteria including basic performance characteristics to ensure consistency and fairness in competition. The standards are normally applied to new balls to ensure manufactured product meets the expected quality for tournament play, however these same guidelines provide an excellent standard against which used balls can be compared, as they degrade with age and use. Players want to practice and play recreationally with quality balls without having to open a new canister every time they step on the court. The bounce of the ball is a critical performance characteristic for tennis, where every shot is allowed (and at most times required) to bounce off the court surface. This bouncing off a surface will henceforth be referred to as “rebound” (more complete definition below).
The ability of a ball to rebound well after impacting a surface is the most common test players use to determine that a tennis ball is fit for play. If a ball appears to have lost its ability to rebound to a minimally tolerable height, it is retired from the game, and most of these are discarded in the trash. It is estimated that between 300 and 500 million tennis balls are discarded every year (based on manufactured quantity estimates). Samples of discarded balls taken from indoor tennis club practice carts show that as many as 80% of the balls discarded might still meet the ITF Rebound standard for play if they were tested (other criteria of the ITF standard notwithstanding). However, the process for testing rebound performance of a tennis ball per the ITF standard requires specialized testing equipment and is a time and labor intensive task most people or clubs are not prepared to perform.
This problem is experienced by recreational players and professionals alike, and magnified further for tennis facilities who utilize and manage large quantities of balls. So there are few options available to check a large batch of balls: tediously bounce each ball to see if it is still play worthy, or do a hand “squeeze test” (proven inaccurate), or use one or several commercially available devices to squeeze them (also highly inaccurate). The most common choice is to just replace entire batches of balls periodically to ensure consistent quality. This results in far too many balls being discarded into landfills where they take an estimated 400 years to decompose. It is also a waste for some to be discarded before they have been exhausted of their useful life. This situation is the main reason many perfectly usable tennis balls are not widely re-used. It is simply too difficult and costly to separate the good balls from the bad ones.
Because of this, used balls are rarely collected and less often sorted. Where used balls are accumulated for resale, they are normally sold as-is with the good and bad mixed together which only tends to reduce their value in the marketplace.
There is no industry solution for how to accurately determine which balls in a large batch of balls are compliant with rebound guidelines, nor has any prior art been found to address how to perform such a determination (whether accurate or inaccurate) in any efficient or cost-effective manner. The need clearly exists for an easy and inexpensive way to separate balls into a number of rebound performance grades. A solution to sorting used balls creates a new incentive in the recycling industry to collect large batches of balls which can then be properly and affordably recycled. Such capability makes possible the much desired environmental conservation practices, which are: REDUCE, REUSE, and RECYCLE.